The technology relates to a spark-ignited internal-combustion engine having a fuel-injection valve that directly injects fuel in a cylinder, and an ignition plug that ignites a mixture of fuel and air in the cylinder with a spark. In particular, the technology relates to an idle speed control at cold start, which requires early warming-up of a catalytic converter in an exhaust system.
As disclosed in Japanese Unexamined Patent Application Publication No. 2004-270504, during an idle operation of an internal-combustion engine, an idle speed control (hereinafter, referred to as ISC control) is executed to provide a feedback control for the degree of opening of a throttle which adjusts an amount of intake air so that an engine speed corresponds to a target idle speed.
Also, Japanese Unexamined Patent Application Publication No. 2005-214039, assigned to the assignee of the present application, discloses a catalyst warm-up method for the spark-ignited internal-combustion engine of in-cylinder direct-injection type including the steps of, when the early warming-up of the catalyst is requested, setting the ignition timing to be at compression top dead center (TDC) or later, and setting the fuel-injection timing at the TDC or later and immediately before the ignition timing, for performing super retard combustion.
The above-described super retard combustion is a technique for increasing the exhaust temperature due to combustion in an exhaust path by retarding the ignition timing to be the TDC or later so as to decrease the combustion rate and the combustion efficiency. In the super retard combustion, the degree of opening of the throttle is relatively increased in the idle operation to compensate for the decrease in torque caused by the decrease in the combustion efficiency, as compared with normal combustion in which the fuel-injection timing and the ignition timing are before the compression top dead center.
While in super retard combustion the exhaust temperature is extremely high, but it can be further elevated if the amount of fuel injection and the amount of intake air are increased in accordance with the increase in load of an auxiliary device and the like such that the combustion quantity is further increased. Therefore, the temperature of the catalytic converter may become excessively high, causing thermal damage and thermal degradation.